Windcatcher
with double domes and windcatchers in the central desert city of Naeen, near Yazd.]] A windcatcher (Persian: بادگیر Bâdgir, or Malqaf / Malgaf in Arabic) is a traditional Persian architectural device used for many centuries to create natural ventilation in buildings. It is not known who first invented the windcatcher, but it still can be seen in many countries today. Windcatchers come in various designs: uni-directional, bi-directional, and multi-directional. Examples of windcatchers can be found in traditional Persian-influenced architecture throughout the Middle East, Pakistan and Afghanistan. Background Central Iran has a very large day-night temperature difference, ranging from cool to extremely hot, and the air tends to be very dry all day long. Most buildings are constructed of very thick ceramics with extremely high insulation values. Furthermore, towns centered on desert oases tend to be packed very closely together with high walls and ceilings relative to Western architecture, maximizing shade at ground level. The heat of direct sunlight is minimized with small windows that do not face the sun. Function The windcatcher or malqaf can function by several methods: One of the most common uses of the malqaf is as an architectural feature to cool the inside of the dwelling, and is often used in combination with courtyards and domes as an overall ventilation / heat management strategy. The malqaf is essentially a tall, capped tower with one face open at the top. This open side faces the prevailing wind, thus 'catching' it, and bringing it down the tower into the heart of the building to maintain air flow, thus cooling the interior of the building. This is the most direct way of drawing air into the building, but importantly it does not necessarily cool the air, but relies on a rate of air flow to provide a cooling effect. This use of the malqaf or windcatcher has been employed in this manner for thousands of years, as detailed by contemporary Egyptian architect Hassan Fathy. The second usage is in combination with a qanat, or underground canal. In this method however, the open side of the tower faces away from the direction of the prevailing wind. (This can be adjusted by having directional ports at the top). By closing all but the one facing away from the incoming wind, air is drawn upwards using the Coandă effect, similar to how opening the one facing towards the wind would pull air down into the shaft. As there is now a pressure differential on one side of the building, air is drawn down into the passage on the other side. This hot air is brought down into the qanat tunnel, and is cooled by the combination of coming into contact with the cold earth (as it is several meters below ground, the earth stays continuously cool) as well as the cold water running through the qanat. The air is therefore cooled significantly, and is then drawn up through the windcatcher by the same Coandă effect. This therefore brings cool air up through the building, cooling the structure overall, with the additional benefit that the water vapour from the qanat has an added cooling effect. Finally, in a windless environment or waterless house, a windcatcher functions as a solar chimney. It creates a pressure gradient which allows less dense hot air to travel upwards and escape out the top. This is also compounded significantly by the day-night cycle mentioned above, trapping cool air below. The temperature in such an environment cannot drop below the nightly low temperature. These last two functions have gained some ground in Western architecture, and there are several commercial products using the name windcatcher. When coupled with thick adobe that exhibits high heat transmission resistance qualities, the windcatcher is able to chill lower level spaces in mosques and houses (e.g. shabestan) in the middle of the day to frigid temperatures. So effective has been the windcatcher in Persian architecture that it has been routinely used as a refrigerating device (yakhchal) for ages. Many traditional water reservoirs (ab anbars) are built with windcatchers that are capable of storing water at near freezing temperatures for months in summer. The evaporative cooling effect is strongest in the driest climates, such as on the Iranian plateau, hence the ubiquitous use of these devices in drier areas such as Yazd, Kashan, Nain, and Bam. This is especially visible in ab anbars that use windcatchers. A small windcatcher (badgir) is called a "shish-khan" in traditional Persian architecture. Shish-khans can still be seen on top of ab anbars in Qazvin, and other northern cities in Iran. These seem to be more designed as a pure ventilating device, as opposed to temperature regulators as are their larger cousins in the central deserts of Iran. Gallery image:Bad Gir Yazd Dolat Abad.jpg|The windcatcher of "Dowlat-abad" in Yazd, is one of the tallest extant windcatchers. image:Borujerdiha.jpg|Borujerdi ha House, in central Iran. Built in 1857, it is an excellent example of ancient Persian desert architecture. The two tall windcatchers cool the andaruni section of the house. Image:Wind Tower Dubai.jpg|The tower on this Barasti made (Palm Fronds) house catches the wind in the same way as a normal wind tower and cools the interior Wind Catchers in the Persian Gulf Countries The emergence of a traditional Bahraini and Persian Gulf style of architecture arose as people migrated to Bahrain with the growth of the pearl trade. With newfound wealth, the merchants built houses of note in the 18th and 19th centuries. The people of Fars in Iran, for example, came and brought with them their Persian architectural designs, including the distinctive wind tower which can be seen so prominently in the Awadiya area (after their hometown Evaz in Iran and elsewhere in Bahrain. This distinguishing feature was adapted locally with its own distinctive decorative motifs. The wind tower, an early and very effective form of air conditioning, has in fact been around for about 500 years and was developed from early wind scoops first built about 2,000 years ago in Iran. In Muharraq and also in parts of Manama there are many buildings, which are no more than two stories high and houses built with natural ventilation, using wind towers and badghirs, the devices for speeding up the flow of air and which consists of horizontal slats in the lower part of the walls. Badghir means ‘wind trap’ and is also the word used to describe the wind tower. See also *Persian architecture *Yakhchal *Solar chimney *Qanat References External links *Hassan Fathy: "Natural Energy and Vernacular Architecture" http://www.unu.edu/unupress/unupbooks/80a01e/80A01E00.htm#Contents * * * *Yazd, the city of windcatchers. *The famous Dowlat-abad windcatcher in Yazd *Windcatchers are incorporated into the architectural expression of traditional Persian buildings. Notice this sample, with 6 symmetrical badgirs, in Yazd. *ventilation cowl on a ship Category:Cooling technology Category:Iranian architecture Category:Islamic architecture Category:Low-energy building Category:Architectural elements Category:Appropriate technology ar:ملقف de:Badgir es:Captador de viento eo:Ventokaptilo fa:بادگیر fr:Badgir it:Torri del vento nl:Windvanger